1. Field of the Invention
The present specification relates to an orthopedic device, and, more specifically, to an adjustable length orthopedic device.
2. Description of the Related Art
The intramedullary rod or nail (“IMR” or “IMN”), also known as Küntscher nail, is a rod placed into the medullary cavity of a bone. These rods have been used to treat fractures of long bones of the body, including the tibia, femur, humerus, and others. IMNs result in earlier return to activity and are “load-sharing” which helps a person place weight on the affected extremity sooner.
The intramedullary nail was initially used by Küntscher in 1939 for use in soldiers in World War II. His design consisted of a long, slender metal cylinder with an open, “cloverleaf” profile. When inserted in medullary canal of a fractured long bone, the nail was then responsible for all load-bearing in the bone as well as stabilizing the fracture site during healing. While innovative, this nail's open profile meant it had very little torsional stability, and a lack of locking screws meant the bone fractures and the nail could move relative to each other and disrupt healing. Since then, the IM nail has undergone radical changes to make it stronger and more stable inside the bone. Contemporary nails now have a closed, cylindrical cross-section and holes for locking screws on the proximal and distal ends of the nail. Patients who receive an IM nail can regain normal use of their limb within 1-2 weeks. The procedure of implanting the nail is minimally invasive and the infection rate is extremely low.
An additional application of the IM nail is to lengthen children's limbs in cases of limb-length discrepency. In these cases, the nails only extend and are not intended to be used with a fractured long bone.
Currently available IM nails are much stronger (in bending stiffness) than the intact bone. Given that bone remodels in response to load, with fundamentally stronger nail inserted, the surrounding bone will decrease its own strength accordingly. Another issue is failure of the locking screws due to repeated concentrated stresses on the screws. Further, because of human size variability there are differences in the length (and width) of the nails which typically requires the stocking of multiple length nails and may require left and right sided devices as well. Since bone length varies with the individual, surgery centers must currently keep an inventory of over 100 different sizes of the same IM nail (see TABLE 1). Furthermore, the sizes are discrete (not continuous), which makes the fit approximate for a substantial proportion of the population. This problem is also manifested in the operating room, when the surgeon must a priori select one nail from inventory for implantation; if the measurement is inaccurate (perhaps due to a highly comminuted fracture), the originally-selected nail must be discarded, creating waste. Post-operative complications of inserting an incorrectly-sized implant include fracture at the time of surgery or insufficient fixation.
TABLE 1Example Dimensions for Tibial NailsMinimumMaximumMinimumMaximumNumberLengthLengthDiameterDiameterof NailNail(mm)(mm)(mm)(mm)SizesM/DN Tibial180460615127Nail(Zimmer)Expert Tibial25545081398Nail (Synthes)Phoenix2404207.513.595Tibial Nail(Biomet)T2 Tibial Nail24042091591(Stryker)ALOD25042010101(exampledimensions)
Recent advances have modified the conventional nail to change its diameter to fit differently sized medullary canals, yet no reports exist of an IM nail that is adjustable in length. The practical significance of creating a functional intramedullary nail that can adjust its length to match the lengths offered by currently used nails is that surgery centers will reduce their inventory and manufacturers will see decreased production costs. With the ALOD, inventory would be reduced.
Lag and locking screws are frequently used in fracture fixation and other orthopedic surgeries. Like the IMNs, these are manufactured in an array of discrete sizes, which may not be appropriate for any given patient. If the screws used are improperly-sized for the application, there can be intra-operative and post-operative complications. Using a screw that is too long can interfere with tendon gliding if the distal end of the screw exits the cortex; using a screw that is too short can create inadequate purchase into the cortex and thus not have sufficient structural integrity for healing. In either case, additional surgeries may be required to remedy.
Accordingly, there is a continued need for fracture fixation devices that can be easily customized to give a patient-specific fit during orthopedic surgery.